The general purpose of this project is the use of specific antibodies as tools in delineating native conformation in proteins and in indicating biosynthetic relatedness among protein species. Antineurophysin-Sepharose matrices (previously reported) have been used to isolate proteins immunologically related to the neurophysins including precursors to the neurophysins if they exist. High molecular weight species binding to the column were investigated by gel electrophoresis, isoelectric focusing and amino acid analysis. An unexpectedly low cysteine content indicated the need to investigate the specificity of antibodies for native conformation. This question is being pursued by radioimmunoassay studies of antibody binding to neurophysins in denatured states. Antibodies prepared against thermolysin and two large fragments of this protein have been used in immunodiffusion assays and radioimmunoassays to study conformational properties of the native protein as well as the fragments. Affinity chromatographic techniques have been used to isolate ribonuclease antibodies specific for the S-peptide region (residues 1-20). Competition experiments have been carried out to determine the precise specificity of the antibodies for use in characterizing semisynthetic sequence analogues.